
2-9
SIMATIC 545/555/575 System Manual
Pre-installation Guidelines
In Figure 2-5, relay CRM is the interposing relay, and FLT is a 24-volt relay,
in the low-voltage safety chain. Note the use of pushbutton switches for
master stop (normally closed) and master start (normally open). Power to
the safety-critical loads is not applied until the master start switch is turned
on. If the master stop switch is turned on, then the safety-critical loads are
turned off. If one of the fault relays opens, then the safety-critical loads are
also turned off. Refer to Section 2.2 for more information on safety
considerations.
FLT
CRM
CRM
Master Stop
PB
Master Start
PB
F1
F2
F3 F4 F5
P/S
C
P
U
C
P
U
C
P
U
FLT
CRM
Output
Modules
575 VME System
L1
L2
24V115V
Figure 2-5 Safety Chain Controlling Outputs Example
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